We plan to study the anatomic effects of experimental hemorrhagic shock in dogs on the cardiovascular system, and especially on the heart. The effects of exogenous norepinephrine treatment on the heart during shock will be determined, and quantitative measurements of lesion formation will be made. We will study a possible "no reflow" effect on the heart, with measurements being made by the labelled microsphere technic of regional myocardial blood flow. The effects of mannitol on blood flow and on lesion formation will be determined.